The key word there being "try."
Pretty much. No one said you can't try to tactically retreat, but the wobbly wizard ain't likely to outrun a Barbarian( monk or anyone if he also stop to shot), and once he is pined down(engaged) he can try to turn away and run(disengage), but he is far more likely to get intimate with Barbarian sword.
No, he should be able to straight up kite the barb. For example: Encounter starts and the barb rushes the mage. The mage seeing this casts Web. The barb is webbed and the mage puts some space between them and pew pews him. Next round, uh oh, the barb made his save and is rushing the mage again! Mage casts Grease and the barb is slowed. Mage makes some more space and pew pews him. Etc... See where this is going? If players shrug and simply accept that their range characters (see, its even in the title) get locked down on melee then THATS the failing in the game design, imo.